In glass pressing, the rapid and controlled exchange of heat between the glass and the mold equipment is extremely important. It is particularly important that the temperatures of the mold equipment be kept within a range which is most advantageous for the pressing process. This temperature should be closely below the "sticking" temperature at which the glass tends to adhere to the mold equipment and, on the other hand, the temperature should not be allowed to drop below the optimum forming-temperature range because this may cause optical defects or checks in the product. In the pressing of glass, the rate of heat removal from the molten glass by the mold equipment depends to a large extent on the glass thickness and its geometric shape in localized regions. If the glass item to be produced has regions of both broad flat or slightly curved surfaces and also regions of relatively sharp corners, the rate of heat exchange between the glass and the mold equipment can differ significantly from adjacent ones of such regions to the next. Under such circumstances the conventional cooling systems for plungers used in glass pressing are inadequate in handling the cooling rates in adjacent ones of said regions or zones because present methods of cooling plungers involve a single source of cooled fluid entering the plunger in one single chamber, being distributed in various locations and generally collected at a single location with resultant individually varying return flow paths which affect one another causing arbitrary and undesirable side effects in the cooling system design and in plunger thermal performance.
In order to overcome the above discussed deficiencies in the pressing of glass items with substantial geometric shape variations such as those mentioned, the present plunger cooling system has been developed and, accordingly, it is an object of the present invention to provide a method of and apparatus for independently obtaining regional or localized control of temperatures on the exterior or glass pressing surfaces of plungers used for pressing glass articles with significantly large variations in the geometric configurations of different regions or zones thereof, such as, for example, articles having relatively sharp corners.
Other objects and characteristic features of the invention will become apparent as the description proceeds.